The present invention relates to a novel process for preparing a normal long chain alkanoic acid. Particularly, this invention relates to a novel process for preparing a normal long chain alkanoic acid having more than 26 carbon atoms by adding a trihalogenomethane to a normal alpha-olefin (I) having more than 25 carbon atoms in the presence of a radical initiator to form a 1, 1, 1-trihalogenoalkane (II) having more than 26 carbon atoms, and then hydrolyzing the compound (II) in an alkaline medium into the normal long chain alkanoic acid (III) having more than 26 carbon atoms.
The normal long chain alkanoic acids having more than 26 carbon atoms are useful as intermediate materials for producing agricultural chemicals and pharmaceuticals, and normal long chain alkyl alcohols obtainable by reducing such a normal long chain alkanoic acid, for instance, triacontanol has recently been given attention as a compound having a growth-controlling function to plants and fungi belonging to the class Basidiomycetes.
As a method for synthesizing a normal higher alkane-carboxylic acid, methods have hitherto been known in which at first a ketoacid is synthesized as an intermediate substance and it is reduced to be the normal long chain alkanoic acid, and the methods are reported in literatures, for instance, R. G. Jones, J. Am. Chem. Soc., 69, 2350 (1947); A. Watanabe, Bull. Chem. Soc., Japan, 32, 1295 (1959); A. Watanabe, ibid., 33, 531 (1960).
However, it is hardly said that the above-mentioned methods are idustrially applicable methods because of its use of a specified raw material and of the plurality of steps of the above-mentioned method including complicated reactions.
The inventors, considering the above-mentioned problems, studied the possible methods for producing ther normal long chain alkanoic acid from an easily available raw material in a few number of steps in excellent yield, and then have arrived at this invention.
The production of a normal long chain alkanoic acid according to this invention is indicated by the following reaction formulae: ##STR1##
This is, the present invention offers a novel process for preparing a normal long chain alkanoic acid having 26 to 36 carbon atoms, comprising: bringing a trihalogenomethane into reaction with a normal alpha-olefin having 25 to 35 carbon atoms in the presence of a radical initiator to obtain a 1,1,1-trihalogenoalkane; and hydrolyzing said 1,1,1-trihalogenoalkane with an alkali thereby to obtain said normal long chain alkanoic acid. For instance, a normal alkyl halide is cross-coupled with 1-halogenoundecene-10 in a Grignard's reaction to obtain a normal alpha-olefin (I). The normal alkyl halide is represented by the formula: CH.sub.3 (CH.sub.2).sub.n CH.sub.2 --X wherein X is Cl, Br or I; and n is an integer of from 12 to 22. The normal alpha-olefin produced in petrochemistry may be used as the compound (I). The compound (I) is reacted with a trihalogenomethane in the presence of a radical initiator to obtain 1,1,1-trihalogenoalkane (II) having 26 to 36 carbon atoms, and then the compound (II) is hydrolyzed in an alkaline medium to convert into a normal long chain alkanoic acid (III) having 26 to 36 carbon atoms. The followings are the detailed explanation of the present invention.
The normal alpha-olefin having more than 25 carbon atoms (I) for use in this invention is, for instance, obtained by the above-mentioned step (1) or obtained by polymerizing ethylene.
As an example of the step (1), either a normal alkyl halide having more than 14 carbon atoms (represented by the formula: CH.sub.3 (CH.sub.2).sub.n CH.sub.2 --X), or 1-halogenoundecene-10 may be converted into the corresponding Grignard reagent. The Grignard reagent is made to cross-couple with either 1-halogenoundecene or the normal alkyl halide. As the starting material, normal alkyl halide having 14 to 24 carbon atoms and Cl, Br or Cl as a halogen, preferably Cl or Br.
In addition, the 1-halogenoundecene-10 is 1-chloroundecene-10, 1-bromoundecene-10 or 1-iodoundecene-10. The above-mentioned cross-coupling is carried out in an ether-type solvent, for instance, diethyl ether or tetrahydrofuran at a temperature of -78.degree. to 30.degree. C., preferably of -10.degree. to 15.degree. C. In order to carry out the cross-coupling smoothly, it is preferable to add a copper compound, for instance, CuBr or Li.sub.2 CuCl.sub.4 to the reaction system. The amount of the addition is 0.1-1.0 mol of the compound per mol of the Grignard reagent.
The addition of the normal alpha-olefin to the trihalogenomethane of this invention is carried out according to the step (2) above-mentioned. As the trihalogenomethane represented by the formula CHX.sub.3, chloroform, bromoform or iodoform is used. The above-mentioned addition reaction may be also carried out at a raised temperature, however, for fear of the frequent side reactions, it is preferably carried out at a relatively low temperature, for instance, 40.degree. to 100.degree. C. for at least longer than 5 hours. The radical initiator is not necessary limited and, for instance, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, azobisisobutyronitrile or ultraviolet rays may be used. The amount of the radical initiator is preferably 0.05 to 0.15 mol per mol of the normal alpha-olefin (I) for use in the reaction.
The intermediate product of Example 1 of this invention, i.e., 1,1,1-trichlorotriacontane, CH.sub.3 (CH.sub.2).sub.28 --CCl.sub.3, is a novel compound.
The step (3) is hydrolysis of a 1,1,1-trihalogenoalkane (II) having more than 26 carbon atoms and, via this step, a normal long chain alkanoic acid is produced.
The hydrolysis of this invention does not so easily proceed as in the cases of lower trihalogenoalkanes. Using an aqueous alkali solution at a temperature of 100.degree. C., the reaction did not proceed substantially in the case of compound (II) within 20 hours. On the other hand, the reaction proceeds by the use of an acid catalyst such as sulfuric acid and nitric acid. However, in this case, the yield of the object compound is poor because of the formation of by-products in large amounts. Further, in the case where the reaction is carried out in a uniform solvent mixture such as a system of dimethylsulfoxide and an aqueous alkali solution, although the reaction proceeds, it is also difficult to obtain the object alkanoic acid in high yield due to the accompaniment of de-carboxylation of the carboxylic acid formed.
Meanwhile, the carrying out the hydrolysis of trihalogenoalkane in the interphase between an organic phase and an aqueous phase, the object alkanoic acid is obtained extremely effectively. Actually, in the case where an organic solution containing the dissolved trihalogenoalkane and an aqueous alkali solution are made to react under agitation, the object product is obtained from the reaction mixture in a state of suspension or emulsion.
Although the reaction mechanism has not been elucidated, however, such a phenomenon is presumably attributed to the structure of higher order and the specific properties of the chain compound with a large number of carbon atoms.
In the present invention, the hydrolysis is generally carried out at a temperature of 20.degree. to 120.degree. C., preferably 40.degree. to 100.degree. C. Higher the temperature, the fear of de-carboxylation is the larger, and lower the temperature, the longer the time period for completion of the reaction.
As the alkali, a hydroxide of an alkali metal such as sodium hydroxide, potassium hydroxide, etc. may be used.
As the organic solvent for use in the present invention, the solvent which is not completely miscible with water is preferable. For instance, that is an alcohol such as n-butyl alcohol, isobutyl alcohol, 1-pentanol, isoamyl alcohol, sec-amyl alcohol, 3-pentanol and tert-amyl alcohol. Furthermore, that is a saturated hydrocarbon having a relatively low boiling point such as butane, pentane and hexane. In addition, an emulsifier may be added to the reaction system.
As has been described above, the present invention has made it possible to easily obtain a normal long chain alkanoic acid having more than 26 carbon atoms, useful as a raw material for producing the normal long chain alcohols used as an intermediate product for agricultural chemicals and pharmaceuticals or the plant-growth controlling agent, and accordingly the present invention has contributed much in industrial and agricultural fields.